Cathode arrangements for getter ion pumps



1970 J. A. VAUMORON EI'AL I 3,496,400

CATHODE ARRANGEMENTS FOR GETTER ION PUMPS Filed Feb. 19, 1968 .J A/y A. vounoxmv,

LAURGIW'E Mum-usual,

INVENTORJ /QZZ T ATTORNEY United States Patent U.S. Cl. 313-174 14 Claims ABSTRACT OF THE DISCLOSURE A cathode arrangement for a getter ion pump having a metal backing plate upon which is mounted one or more grid formed sheets of getter material. The back surface of each sheet facing said backing plate is inactive in sustaining a discharge in a getter ion pump and these surfaces are available for deposition of sputtered material from an active surface of said backing plate or another of said sheets. The sheets may be expanded sheets of getter material and where there are more than one the grid intersections of one sheet overlie the grid interspaces of the next sheet. In this case the backing plate may be a non-getter or a getter material.

This invention relates to cathode arrangements for getter ion pumps employing the penning discharge.

This type of pump is normally of a structure including a pair of parallel cathodes separated by an anode which is either of a grid or cellular construction. A high potential is applied between the anode and cathodes and the pump body is placed in a magnetic field parallel to the electric field, the influences of the two types of field combining to sustain a gas discharge down to a very low pressure in the region of 10 torr. The discharge sputters the cathodes and some getter material is deposited on the anode which takes up active gases. The sorption of inert gases, however, is more complex, the significant effect being the formation of gas ions which are driven into the cathode surfaces by the electric field. While this results in a considerable pumping effect when a new pump is used, after continued use the inert gases are re-emitted by sputter erosion of the cathode so that eventually the net pumping action for inert gases becomes negligible using an ordinary diode penning pump.

Inert gas pumping has thus been given consideration in the past and two particular arrangements have been derived for its improvement. The first one comprises the addition of an extra electrode maintained at a negative potential with respect to the anode, the arrangement being such that this extra electrode receives a net buildup of sputtered cathode material. The second arrangement involves the use of special forms of cathode or anode which cause inactive cathode regions in which a net buildup of sputtered material occurs.

The terms active and inactive as used with reference to cathode surfaces in this specification refer to those surfaces of a cathode arrangement which respectively do or do not assist in the sustenance of a cold cathode discharge during use of an associated getter ion pump, the active and inactive surfaces being directionally opposed to one another.

According to the present invention acathode arrangement, for a getter ion pump, comprises at least two components of getter material, one of the components being a grid formed sheet so that, in use of a pump employing the arrangement, material sputtered from an active sur- 3,496,400 Patented Feb. 17, 1970 ICC face of the other component is deposited on the inactive surface of the said sheet, being a surface facing the said active surface.

Further according to the present invention a cathode arrangement for a getter ion pump comprises a metal backing plate to the active surface of which is attached a grid-like structure of getter material which includes at least one grid formed sheet so that, during use of a pump employing the arrangement, material sputtered from an active surface of the arrangement is deposited on the inactive surface of the or each sheet, being that surface of the or each sheet which faces towards the backing plate.

In one arrangement the grid-like structure comprises a. single grid formed sheet, in which case the backing plate must be a getter material.

Preferably however, there is a plurality of grid formed sheets of getter material which are mounted one upon the other so that the grid intersections of one sheet overlie the grid interspaces of the next. When the sheets comprise expanded sheet of a metal, such as titanium, an advantage lies in that their slightly contoured surfaces enables them to be mounted directly upon each other and still to have relatively large inactive areas available for deposition of sputtered material. Slotted sheets, however, may also be used.

If overlapping sheets are employed, as indicated above, the backing plate may comprise a non-getter such as stainless steel which has certain economic and structural advantages.

Further advantages may be obtained if the grid formed sheets comprise different getter metal. Thus, if one sheet comprises titanium and another sheet copper, the sputtered titanium provides means of pumping the residual gases by chemical combination and the copper, with its higher sputtering rate, provides a blanket film to trap or bury the ionically pumped gases.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawing which shows an exploded view of a cathode arrangement constructed in accordance with the invention.

Referring now to the drawing, the cathode arrangement comprises a flat cathode backing plate 1 and two expanded sheets 2 and 3. Each of these components is made of titanium. Sheets 2 and 3 are spot Welded to each other and sheet to plate 1, thereby giving good electrical connection, and the intersections of the expanded sheet 3 overlie the interspaces of sheet 2. As the expanded sheets naturally have slightly contoured surfaces the spot welding together of the sheet does not prevent sheet 3 from presenting a large portion of its back surface to the front surface of sheet 2, as indeed plate 2 presents its back surface to plate 1. The expanded sheets are attached to the active surface of plate 1, that is to say the surface which faces the anodes when the arrangement is mounted within a pump.

When such a pump is being operated, ions penetrate the grid structure and sputter the backing plate as well at the active surfacesi.e. those facing the anodeof expanded sheets 2 and 3. This sputtered material is deposited, without being re-sputtered, on the inactive regions of the cathode arrangement which include a fairly large proportion of the backing plate 1 and the major portions of the sides of sheet 2 and 3 which face the backing plate. Thus, each sheet 2 and 3 is being used with maximum efiiciency as one active face assists the discharge and is sputtered while the other inactive face allows deposition of the sputtered material.

It has been found that at high pressures material is not sputtered from the cathode backing plate so that if a pump is to be used at these pressures the back plate need not be made of a getter material. The use of stainless steel is particularly suitable as it is cheaper than most getters and has certain constructional advantages.

While the cathode arrangement above is shown and described as having two grid-like sheets, it will be clear that a larger number of such sheet may be employed. The material titanium has been described out of preference and convenience only and may be replaced by any other suitable getter. As already mentioned, the grid sheets may comprise different getter metals with different sputtering rates, such as titanium and copper. Slotted or otherwise apertured sheets may be used, though less advantageously, instead of expanded sheets.

With a diode penning pump having a cellular anode and two cathode arrangements as described a measurable pumping speed for inert gases up to a pressure 3 l0- torr has been obtained. The pumping speed for inert gases is of the order of 10% of that for air at l torr. The structure described provides a simple, clean and robust cathode arrangement.

The cathode arrangement described above is suitable for a penning pump having a cellular anode and two parallel cathodes, one on either side of the anode, arranged at right angles to the axes of the anode cells. The electrons are normally caused to have extended spiral paths by applying a magnetic field along the cell axes. However, the invention can also be applied to what is known as the triode type of pump in which the two cathodes are at differing potentials so that the less nega tive cathode receives more sputtered material than it loses. The term triode pump is also used with reference to pumps in which both cathodes are at the same potential but are each made of a mesh instead of being solid. In this case the anode and pump body are usually maintained at earth potential. The present invention can be employed in this type of pump by using a double layer of expanded getter metal for each cathode. The function of these cathodes is, clearly, similar to that described above so that sputtered material is deposited on the inactive surface of one of the expanded sheets. Again, the two layers may comprise different materials such as titanium and copper or silver.

We claim:

1. A cathode arrangement, for a getter ion pump, of the type having a solid backing plate and including in combination:

(a) a first component of getter material, said component comprising a first grid formed sheet mounted on said backing plate and having a first inactive side; and

(b) a second component of getter material, having a second side which is active;

and in which said first and second sides are directionally opposed to one another.

2. A cathode arrangement according to claim 1 in which said second component of getter material constitutes said backing plate.

3. A cathode arrangement according to claim 1 in which said second component of getter material comprises a second grid formed sheet, said first and second grid formed sheets having intersections and interspaces and in which said first and second grid formed sheets are mounted upon each other, said intersections of one of said sheets overlying said interspaces of said other of said sheets.

4. A cathode arrangement according to claim 3 in which said first and second grid formed sheets are expanded sheets of getter material.

5. A cathode arrangement according to claim 3 in which said backing plate is a non-getter.

6. A cathode arrangement according to claim 5 in which said backing plate is stainless steel.

7. A cathode arrangement, for a getter ion pump, comprising in combination:

(a) a metal backing plate having an active surface;

and

(b) a grid-like structure comprising a plurality of grid formed sheets of getter material mounted in a stack upon said active surface of said backing plate, each of said sheets having intersections and interspaces and the intersections of individual ones of said sheets overlying or underlying the interspaces of the next sheet in said stack.

8. A cathode arrangement according to claim 7 in which said backing plate is a non-getter.

9. A cathode arrangement according to claim 7 in which said sheets are expanded sheets of getter material.

10. A cathode arrangement according to claim 7 in which alternate sheets in said stack comprise a first getter material and the remaining sheets in said stack comprise a second getter material, said first and second getter materials having different sputtering rates.

11. A cathode arrangement according to claim 9 in which said first getter material comprises titanium and said second getter material comprises copper.

12. A cathode arrangement for a getter ion pump comprising a backing plate of getter material and an expanded sheet of getter material mounted on said backing plate.

13. A cathode arrangement for a getter ion pump comprising a plurality of grid formed sheets of getter material mounted upon each other, each sheet having grid intersections and interspaces and the intersections of alternate ones of said sheets overlying the interspaces of the remaining one of said sheets.

14. A cathode arrangement according to claim 13 in which each of said sheets is an expanded sheet of a getter material.

References Cited UNITED STATES PATENTS 2,208,987 7/1940 Kuhne et al. 313174 2,351,026 6/1944 Ewing 313174 X 3,187,885 6/1965 Hansen et al. 206.4

3,422,299 l/ 1969 Morehead 313l74 FOREIGN PATENTS 1,000,535 1/1957 Germany.

JOHN W. HUCKERT, Primary Examiner ANDREW J. JAMES, Assistant Examiner Us. 01. X.R, gee-.4; 313176, 178, 

